An open head mount display (HMD) device is also referred to as a glasses display device, which is wore in front of user's eyes in a similar way to wear a helmet or glasses so that the user can simultaneously see an external object 91 and a display image 92, as shown in FIG. 1.
As shown in FIG. 2, an existing open head mount display device comprises a display unit 1 for displaying an image for user's eyes 8. Preferably, two display units 1 are provided and used for respectively providing different display images for the user's eyes 8 so that a 3D display is achieved. The display unit 1 generally comprises a display (e.g., liquid crystal display) 11 and a focusing lens unit 12, wherein the display 11 is used for generating a display image, the focusing lens unit 12 is used for adjusting an object distance of the display image with respect to the user's eyes 8, that is, for changing light divergence degree of the display image, so that the display image is “simulated” as an image displayed far away from the user's eyes 8, thus enabling the user to view the display image comfortably, and the object distance of the display image 92 with respect to the user's eyes 8 is equal to an object distance of the external object 91 with respect to the user's eyes 8, thus ensuring that the user can simultaneously see the display image 92 and the external object 91 clearly. The focusing lens unit 12 generally comprises one or more focusing lenses. The object distance of the display image 92 with respect to the user's eyes 8 may be changed by adjusting positions of the focusing lenses whose the specific structure and the adjustment method have been known in the art and will not be described in detail here. In addition, in order to save space, the display 11 is generally provided at two sides of the user's eyes 8 (e.g., in temples of glasses). In this case, the display image 92 should be reflected into the user's eyes 8 by a reflection unit. The reflection unit may be composed of a series of reflection lenses, and the reflection lens located in front of the user's eyes 8 is a transflective lens 21, so that the user is allowed to see the external object 91 while the display image 92 is reflected.
The inventor founds that there are at least following problems for the existing open head mount display device.
First, in the existing open head mount display device, the object distance of the display image 92 with respect to the user's eyes 8 is determined in a manual adjusting manner, resulting in a tedious operation, a poor accuracy, a poor timeliness and a poor display effect.
Secondly, in many cases, the display image 92 is related to the external object 91 (e.g., the display image is an illustration for the external object), this requires that the display image 92 and the external object 91 satisfy specific relationship between positions thereof (e.g., the display image is positioned just beside the external object). However, in the existing open head mount display device, since the position of the external object 91 cannot be determined, the display image 92 only can be displayed at a default position (which refers to a position of the display image in a plane with a same distance from the user's eyes, rather than the object distance of the display image with respect to the user's eyes), but this position (e.g., any position in “up, down, left or right” direction) of the display image 92 in the plane with the same distance from the user's eyes 8 may be not appropriate (for example, the illustration for a certain external object may be far away from the external object).
Thirdly, angles between sight lines of the user's two eyes are different when the user views external objects 92 at different distances, wherein, when the user views the external object 92 at a far distance, the sight lines of the user's two eyes are almost parallel to each other, and the closer the external object 92 is, the larger the angle between the sight lines of the user's two eyes is. However, positions of display images provided by the two display units for left and right eyes are fixed, which results that, when the positions of the display images for left and right eyes do not match the angle between the sight lines of the user's eyes, the display images for left and right eyes displayed by the two display units cannot exactly coincide with each other after subjected to user's brain treatment, and there is a ghost in the user's eyes.